Bridges and comparable traffic-carrying structures are provided between abutments and superstructure and/or between subsections of the superstructure with expansion gaps, in order to permit damage-free thermal expansion or contraction of the superstructure. Depending on the size of the bridges in question, expansion gaps within the range of up to several meters are necessary. In order to permit vehicles to travel over the expansion gaps in question, expansion-gap bridging devices are provided.
In this context, the use of multi-plate roadway expansion joints is particularly well known, wherein two bridge parts (in this sense, the abutment is also a “bridge part”) are joined to one another by at least two crossbeams spaced apart from one another, in such a way that the ends of bridge parts in question facing one another can undergo a relative movement toward and away from one another in the longitudinal direction of the crossbeams. Chord plates spaced apart from one another, capable of moving relative to one another and oriented substantially transversely relative to the longitudinal direction of the crossbeams, are braced on the crossbeams, such that their respective top side can be positioned substantially at the level of the roadway of the bridge or can form this, although embodiments are also known in which separate elements forming the traffic-carrying surface are disposed on the chord plates at their top side. If the ends of the bridge parts move toward one another because of thermal expansion in the longitudinal direction of the crossbeams, the spacing between the chord plates decreases. If the ends of the bridge parts move away from one another because of thermal contraction in the longitudinal direction, the spacing between the chord plates increases. Examples of pertinent prior art in this respect can be found in DE 19705531 C2, DE 3514776 C1 and DE 3212717 C1.
In regions threatened by earthquakes, the danger exists of abruptly occurring changes of position of the bridge parts relative to one another (especially in longitudinal direction of the crossbeams or with such a movement component). Under certain circumstances these changes can no longer be compensated by multi-plate roadway expansion joints, because they exceed the working range of the use for which they are intended. It is then conceivable that the bridge parts will move so much toward one another in longitudinal direction, beyond the normal thermal expansions, that the chord plates temporarily bear against one another in certain positions of the bridge parts, and further movement of the bridge parts toward one another results in internal stresses and possible damage to the chord plates or bridge parts. In such cases it is not enough to anticipate that the carrying capacity of the bridge for vehicular traffic is no longer assured after the earthquake; to the contrary, the damage to the bridge parts and/or the expansion-gap bridging device may be so pronounced that the bridge has to be completely rebuilt.
U.S. Pat. No. 5,887,308 A discloses an expansion-gap system for bridges that is designed not only to compensate for longitudinal expansions in travel direction—caused by normal fluctuations of the ambient temperature—but also to withstand seismographic forces occurring in transverse direction relative to the roadway. For this purpose the expansion-gap system comprises a plurality of chord plates spaced apart from one another and capable of displacement, braced on a plurality of crossbeams mounted at their ends in boxes. At one end the crossbeams are respectively movable within bearing boxes in transverse direction relative to the roadway of the bridge, so that forces or displacements occurring in this direction, for example due to an earthquake, lead to corresponding transverse displacements of the crossbeams. A disadvantage is that extremely large changes of the gap width of the expansion gaps occurring during earthquakes can no longer be compensated when the chord plates are already bearing against one another, thus resulting in destruction of the expansion-gap system or detachment thereof from the structure parts, whereby the bridge will no longer be able to carry traffic for the time being after an earthquake.
The foregoing also applies to the expansion-gap bridging device according to U.S. Pat. No. 5,964,069 A. Certainly the entire bridging device therein is raised at one end in order to forestall permanent damage thereto when seismic events cause the gap width of the expansion gaps to narrow beyond the point at which the chord plates bear against one another. Nevertheless, this also prevents the bridge from being able to carry traffic after the earthquake. And the repair work is associated with quite considerable expense, quite aside from the fact that, in the case of a permanent change of position of the structure parts relative to one another caused by the earthquake, even if complete reconstruction of the expansion-gap bridging device is not necessary, at least very expensive adaptation of the expansion-gap bridging device to the new tectonic conditions is needed.
The objective of US 2008/0148499 A1 and EP 1355009 B1 is to alleviate at least part of these disadvantages. Thus EP 1355009 B1 discloses a bridging device for joint gaps between bridge parts of the type mentioned in the introduction that if at all possible is still intended to be capable of carrying vehicular traffic even after an earthquake, albeit to a restricted extent and with considerably greater difficulty. For this purpose, the expansion-gap construction readily permits, within first limits, changes of position of the bridge parts adjoining the expansion gap relative to one another to occur during use for which they were intended. An additional safety device disposed on one of the bridge parts and on the expansion-gap construction is intended to permit position changes of the bridge parts toward one another beyond those limits without destroying the function of the bridging device or separating the expansion-gap construction from the bridge parts. The safety device comprises at least two elements, which are firmly joined to one another but which are separated if a defined limit load is exceeded and then can be moved toward one another in a well-defined way, for which purpose one of the two elements can be firmly disposed on one of the two bridge parts. Depending on the construction of the safety device, it is intended that additional position changes in the direction of the crossbeams and/or transverse movements of the bridge parts toward one another can be compensated. The safety device represents a predetermined breaking point, which necessitates extensive repair actions after the specified limit load has been exceeded in the direction transverse to the chord plates of the expansion-gap construction. Firstly the roadway expansion joint must be restored to its original position. Then certain elements of the expansion-gap construction, including the broken safety device, must be replaced and connections adjoining it must be rehabilitated.
Nevertheless, at least some of the disadvantages depicted hereinabove in connection with U.S. Pat. No. 5,964,069 A also exist in the bridging device according to EP 1355009 B1.